calculate till mate

Smirnov has some great courses, but Calculate till Mate is advanced and at your level should start with GM Secrets and Grandmaster's Positional Understanding. The course names aren't as advanced as they sound and they even have a practical part. GM Secrets essentially teaches you an organized and effective thinking system (such as calculate forcing variations first, principle of the least active piece, etc.) and GM Positional Understanding is mostly bishop play with some pawn play advice before teaching bishop principles.

Also, I mean no offense or embarrassment by posting this, but is a help:

Essentially you need to look at your opponent's threats and analyse forcing moves first. Calculate till Mate will not help you until you fix these gaps in your knowledge and thinking process.

EDIT: I said in the annotations "winning" the pawn when exchange would have been a more accurate term. In any event white is still much better even though he is actually down a pawn (...Nxf2 Kxf2) since black cannot exploit the weak king. Here you must ask yourself how to take advantage of your lead in development because if you don't use it you'll lose it.